Electron tube



M. ARDlTl ELECTRON TUBE Aug. 29, 1950 Filed March 27, 1946 UNI 1,4770

INSULATION ATTORNEY Patented Aug. 29 1950 ELECTRON TUBE Maurice Arditi, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application March 27, 1946, Serial No. 657,413

Claims.

This invention relates to electron tubes of the type in which electrons in'a beam are velocity modulated to produce grouping or bunching of the electrons therein.

In a certain type of electron discharge device, an electron gun is used to produce an electron beam which is passed through the grids or across the gap of a reentrant cavity resonator called the buncher to produce a velocity modulation of the electrons. These electrons'leaving the buncher, travel througheither a retarding field or a drift space which causes the electrons of different velocities to form groups or bunches. These bunches of electrons pass between .the grids of a second resonator, the catcher, and de liver power thereto. The power delivered depends upon a number of parameters including. the degree of bunching of the electrons, the spacing be tween the grids of the catcher, the velocity of the electron beam, and the frequency to which the catcher resonator is tuned. If the spacing between the grids of the catcher departs from the optimum, the bunch of electrons coming into the space between the catcher grids will first ism.-

part power to the catcher and then as they pass 7 out through this area, will abstract considerable power therefrom. This power, taken by the electrons from the catcher, is lost power and reduces efficiency. While it is possible to approximately calculate the proper spacing between the grids of the catcher for a given frequency, if it is desired to operate the tube over a range of frequencies, it becomes necessary to provide some means for effectively varying the spacing between the grids according to the frequency selected. In addition many variables make for deviation from any calculated value of spacing even at a fixed frequency. Varying the spacin between the grids to meet given conditions presents a difficult problem. In accordance with a feature of the present invention, instead of varying the distance between the grids to compensate for differences of frequency or to obtain the maximum power delivery at a given frequency, the velocity of the electrons, as they pass between these two grids, is controlled so as to control the transit angle between the two grids and thus to control the phase of the electrons in the beam. For this purpose I prefer to provide within the space between the twogrids of the catcher a third grid connected to a suitable source of potential which third grid is used to accelerate or control the velocity of the electrons passing between said first two grids.

Another problem, or what perhapsznay behest considered as another aspect of the foregoing problem, is the phenomena due to the fact that the bunched electrons entering between the catcher grids are retarded by the opposing field. These electrons then tend to spread or de-bunch andif a. substantial amount of de-bunching occurs between the two grids, the de-bunched electrons will absorb a certain amount of the power delivered to the catch resonators. Further in accordance with the present invention, I provide for reducing this de-bunching phenomena to a minimum by a celerating the electrons after they have entered the space in-between the two grids of the catcher so that they have a relatively high average velocity and substantially little dcbunching occurs in this space.

An object of the present invention is the provision of an improved electron discharge device.

Another object of the present invention is the provision of more efiicient electron discharge device of the type in which electrons in a beam are velocity modulated and caused to bunch and energy is extracted from said bunch.

Other and further objects of the present invention will become apparent and the invention will be best understood from the following description of embodiments thereof, reference being had to the drawings in which:

Fig. 1 is a schematic diagram of an electron discharge device embodying the present invention; and

Fig. 2 is a schematic diagram of a reflex elec-v tron discharge device embodying my invention. Referring now to Fig. 1, the electron tube there illustrated is conventional for the most part ex cept for the accelerating rid I. The tube may include a heater 2, a cathode 3, a control grid 4 and focusing ring 5 with a smoother grid ,6, and tuning ring 1. These serve to produce and focus a beam and direct it toward the buncher 8 which includes two grids 9 and i9 coupled to each other by a cavity resonator i i and having a loop l2 arranged therein for applying voltages thereto. The electron beam is velocity modu lated as it passes between grids 9 and ill. It then travels through the drift space is so that the electrons tend to become bunched. The drift space is free of any radio frequency field. The electronswhich are now bunched to a greater or lesser extent, depending upon the particular use of the tube, pass through the first grid it of the catcher 15, whose second grid i6 is coupled to its first grid by means forming therewith a cavity resonator i1. I

In accordance with my invention, the grid -;l "is energy takes place in this space.

3 arranged between grids I4 and I6 and has a voltage applied thereto so that it will accelerate the electrons which pass through grid I4. To maintain the drift space I3 as a field-free space, it is preferred to design the grid I so that it is shielded by grid I4 from the drift space. Grid I is preferably so designed that it will not take too many electrons out of the beam. The grid I is connected to a suitable source of direct current voltage IB which direct current voltage is higher than the D. C. voltage of the grids 9, I0, or I4 and I6 The potential difference between grid I4 and grid I may be for example, of the order of several hundred volts or more and is variable so that it may be adjustable to produce the maximum output. The potential of grid I4 is preferably so adjusted that after the accelerated electrons pass it they are completely decelerated by the radio frequency field between grids I4 and I6 so that when they reach grid I6, substantially all their energy has been absorbed by the cavity resonator I5. The electrons passing grid I6 are then collected by a suitable electrode I9.

My invention may also be employed with a reflex type of electron discharge device of the velocity modulation type. Referring now to Fig. 2, there is illustrated a reflex Klystron having the usual electron gun 28 producing a beam of electrons which pass through the grids 2I and 22 respectively, which grids are coupled together by a resonator 23. The electron beam is modulated as it passes through from grid 2I to grid 22 and then enters a decelerating field which is produced by suitable potentials applied to a reflector electrode 24. toward grid 22. During the interval in which the velocity modulated electrons leave grid 22 and return thereto, they become bunched by the decelerating field. In accordance with my invention, I place an additional grid 25 between grids 2i and 22, preferably nearest grid 22. Grid 25 is connected to a positive source of potential 26 which accelerates the returning electrons, in the manner hereinbefore described, so as to adjust for the maximum delivery of energy to the resonator 23.

Special attention should be paid to the electric circuit connecting the grids I4 and I, and 25 and 22, even though no exchange of radio frequency The electron bunches crossing the space between grids I4 and I, or 25 and 22, induce a current in the external connection of said grids. To nullify the radio frequeny potential variation, for example, between grids I4 and I, it is necessary that the circuit coupling these grids present zero impedance between these grids. This may be accomplished, for instance, among other known means by making the space between grids I4 and I part of a transmission line or a resonant cavity so adjusted that the impedance looking from grids I4 and I is zero.

Fig. 1 illustrates one example: grids I4 and I are part of a wavelength coaxial line 2! presenting substantially zero impedance at the grids I4 and I. Another possible way is to use a half wavelength line shorted for radio frequency at its end.

A similar wavelength line 28 is employed for the above-mentioned purpose between grids 22 and 25.

Transmission lines 21 and 28 may also be adjusted to permit a small impedance so that some radio frequency power due to the passage of the electron beam is delivered to the grids and this The electrons are then reflected back 1 power may be used for feed-back purposes, as for example by feeding back this power to the bunching cavity.

My invention may also be employed with multiple cavity Klystrons, and advantage may be taken of the additional velocity imparted to the electrons by the additional grid to obtain a greater output.

While I have described above the principles of my invention in connection with specific apparatus, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention.

I claim:

1. An electron discharge device of the velocity modulation type comprising an electron gun and an additional electrode defining an electron beam path therebetween, means along said beam path for bunchin'g the electrons in said beam, means including two grids adjacent said beam path and spaced therealong for extracting energy from the bunched electrons when they pass therebetween, and separate electrode means about said beam path and between said grids for controlling the velocity of the electrons in the beam between said grids, thereby to determine the transit time of the electrons between said two spaced grids.

2. An electron discharge device according to claim 1 wherein the velocity controlling means comprises means for accelerating the electrons a predetermined constant amount.

3. An electron discharge device according to claim 1 wherein the velocity controlling means comprises a third grid between said two grids in the path of the beam and means connected to said third grid for applying a selected potential thereto for controlling the velocity of the electrons in the beam.

4. An electron discharge device according to claim 1 wherein the velocity controlling means comprises a third grid between said two grids in the path of the beam and adjacent the one of said grids adjacent said bunching means.

5. An electron discharge device according to claim 1 wherein said extracting means includes a cavity resonator in the beam path and provided with apertures for passage of the beam therethrough, said two spaced grids being mounted about said apertures in the path of said beam, and wherein the velocity controlling means includes a third grid between said two grids and means coupled to said third grid for applying a selected potential thereto for controlling the velocity of the electrons in the beam thereby to determine the transit time between said two spaced grids.

6. An electron discharge device according to claim 1 wherein said extracting means includes a cavity resonator in the beam path and provided with apertures for passage of the beam therethrough, said two spaced grids being mounted about said apertures in the path of said beam, and wherein the velocity controlling means includes a third grid between said two grids adjacent the one of said grids adjacent the bunching means and means connected to said third grid for applying a selected potential thereto for controlling the velocity of the electrons in the beam between said two spaced grids.

7. An electron discharge device according to claim 1 wherein the velocity controlling means comprises a third grid between said two grids in the path of the beam, and a source of direct current potential coupled to said third grid for controlling the velocity of the electrons between said two grids.

8. An electron discharge device of the velocity modulation type for ultra high frequency operation comprising an electron gun and a collector electrode defining an electron beam path therebetween, means about said beam path adjacent said electron gun for bunching the electrons in said beam, a cavity resonator about said beam path adjacent said collector electrode and provided with apertures for passage of the beam therethrough, and separate electrode means in said cavity resonator adjacent said beam path for controlling the velocity of the electrons in the beam path through said cavity resonator, thereby to control the transit time of the electrons through said resonator.

9. An electron discharge device according to claim 8 in which said velocity-controlling means is insulatingly spaced from the walls of said cavity resonator and means are provided coupling said velocity-controlling means to said resonator, said means offering zero impedance between said velocity-controlling means and said resonator at ultra high frequencies.

MAURICE ARDITI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,280,026 Brown Apr. 14, 1942 2,323,729 Ryan July 6, 1943 2,408,423 Hartley Oct. 1, 1946 2,416,302 Goodall Feb. 25, 1947 

